1. Field of the Invention
The present invention relates to a stencil printer for effecting printing with a master wrapped around a print drum and more particularly to a method and a device for making the master.
2. Description of the Background Art
A digital, thermosensitive stencil printing system is conventional as a simple printing system. In this simple printing system, a thermal head or similar perforating means perforates a thermosensitive stencil by melting it with heat to thereby make a master. The master is wrapped around a porous, hollow cylindrical print drum. Ink feeding means disposed in the print drum feeds ink to the inner periphery of the print drum while a press roller or similar pressing means presses a sheet or recording medium against the print drum. As a result, the ink is transferred from the print drum to the sheet via the perforation pattern of the master, forming an ink image on the sheet.
A stencil is usually implemented as a laminate made up of a thermosensitive resin film (simply film hereinafter) and an ink-permeable support adhered to the film and implemented as a porous fiber film (usual stencil hereinafter). The porous fiber film is generally formed of flax fibers or a mixture of flax fibers, synthetic fibers and wood fibers. A problem with the usual master is that because the porous fiber support exists just on the film, a great amount of adhesive gathers in the form of webs at positions where fibers overlapping each other and the film contact each other. At such positions, it is difficult for the thermal head to perforate, or cut, the stencil, making the resulting print irregular.
In light of the above, Japanese Patent Laid-Open Publication No. 10-236011 discloses a thermosensitive stencil implemented as a laminate made up of a thermoplastic resin film, a porous resin film formed on one surface of the film, and a porous fiber film formed on the porous resin film and formed of interconnected fibers. The porous resin film refers to a porous film formed by precipitating resin dissolved in a solvent and then solidifying it by way of example. In the porous resin film, fine cavities overlap each other in a complicated structure in the direction of thickness of film. Also, the porous fiber film refers to a film implemented as, e.g., a thin sheet of cotton, flax or similar plant fibers or polyester, polyvinyl alcohol or similar synthetic fibers; the fibers are adhered together and interconnected by intertwining or weaving. With such a configuration, the stencil obviates irregular printing stated above and attains enhanced elasticity and tensile strength, thereby improving image quality.
A master making condition (e.g. perforation energy) and a printing condition (e.g. the kind of ink matching ink-permeability) noticeably differ from the usual stencil to the stencil including the porous resin film stated above. Therefore, when printing is effected with the usual stencil in a condition matching with the stencil including the porous resin film, the resulting print is defective. This is also true when printing effected with the stencil including the porous resin film in a condition matching with the usual stencil.
It is difficult for the operator of the printer to distinguish the kind of the stencil, i.e., the usual stencil and the stencil including the porous resin film by eye. The operator therefore cannot see the setting of an unqualified stencil until at least one print has been produced. In such a case, the operator has to discard or replace a master or set a qualified stencil, resulting in troublesome operation, wasteful stencil consumption, and noticeable down time.
Moreover, even identical stencils including the porous resin film each are different in cavity ratio, i.e., the density of cavities in the porous resin film, depending on the lot. Consequently, the stencils are different in ink permeability, obstructing stable image quality.
Technologies relating to the present invention are also disclosed in, e.g., Japanese Patent Laid-Open Publication Nos. 6-270527 and 10-236011.
It is an object of the present invention to provide a master making method capable of automatically detecting an unqualified stencil before master making to thereby allow it to be replaced or allow settings to be varied and reduce the down time, a mater making device for practicing it, and a stencil printer including the same.
It is another object of the present invention to provide a master making method capable of insuring stable print quality without regard to irregularity in the cavity ratio of a porous resin film, a master making device for practicing it, and a stencil printer including the same.
In accordance with the present invention, a master making device for a stencil printer includes a master making section for perforating a stencil, which includes a support formed on one of opposite surfaces of a thermoplastic resin film, in accordance with image data. A transmission type sensor senses the transmittance of the stencil in a direction of thickness. A controller determines the condition of cavities existing in the stencil in accordance with information output from the sensor and then varies a master making condition in matching relation to the condition. Alternatively, the controller may inhibit master making operation if the stencil is an unqualified stencil.
Also, in accordance with the present invention, a master making device for a stencil printer includes a master making device for perforating a stencil, which includes a support formed on one of opposite surfaces of a thermoplastic resin film, in accordance with image data. A reflection type sensor faces one of opposite surfaces of the stencil. A low-reflectance member faces the reflection type sensor with the intermediary the stencil. A controller determines a condition of cavities existing in the support of the stencil in accordance with information output from the reflection type sensor and then varies a master making condition in matching relation to the condition. Alternatively, the controller may inhibit master making operation if the stencil is an unqualified stencil.
A master making device and a stencil printer including any one of the master making devices described above are also disclosed.